1. Field of the Invention
The present invention relates to a recording and reproducing apparatus for pulse code modulated (PCM) audio data which is suitable for application to an editing-process for manufacturing a record and the like.
2. Description of the Prior Art
When carrying out the editing to produce a record or the like, musical performances recorded on separate channels (tracks) of a record medium by musical instruments are sequentially mixed to provide a sound signal of desired channels, for example, 2 channels. Alternatively, so-called digital-copy is performed, in which a recorded signal on a desired channel is copied to other channel.
FIG. 1 shows an example of a prior-art recording and reproducing apparatus for PCM audio data which performs such an edition (see Japanese Patent Application No. 62-71032). FIG. 1 shows an example of editing in which musical performances recorded on separate channels (tracks) are copied to other channels (tracks) by the sequential mixing-process.
As shown in FIG. 1, there is provided a magnetic tape 1 for edition, and PCM audio data of an original audio signal to be edited is recorded separately on multi channels (multi tracks), for example, 8 channels of the magnetic tape 1. The PCM audio data of multi channels, for example, 8 channels (8 tracks) recorded on the magnetic tape 1 are reproduced by a reproducing head 2. The PCM audio data of, for example, 8 channels reproduced from the magnetic tape 1 by the reproducing head 2 are supplied to a reproducing-system signal processing circuit 3, in which the PCM audio data undergo interleave demodulation, timebase correction, error correction, interpolation and the like.
Reproduced audio data PB developed at the output side of the reproducing-system signal processing circuit 3 is supplied to one input terminal 4a of a cross-fader circuit 4 which performs a cross-fade function or a fade-in and fade-out function. A music signal or the like is supplied to an external signal input terminal 5 from the outside. The music signal or the like applied to the external signal input terminal 5 is supplied to an analogue-to-digital (A/D) converting circuit 6 which converts an analogue signal to a digital signal. Thus, the music signal or the like is made as a PCM audio data IN by the analogue-to-digital converting circuit 6. The PCM audio data IN is supplied to other input terminal 4b of the cross-fader circuit 4, in which it is cross-faded with the reproduced PCM audio data PB. More specifically, in the cross-fader circuit 4, the reproduced PCM audio data PB supplied thereto through the terminal 4a is multiplied with a coefficient, which changes sequentially from 1 to 0, so that the value (level) of the reproduced PCM audio data PB is decreased with time. On the other hand, the PCM audio data IN supplied to the cross-fader circuit 4 through the terminal 4b is multiplied with a coefficient, which sequentially changes from 0 to 1, so that the value (level) of the PCM audio data IN is increased with time. A time period in which the coefficient changes from 1 to 0 or vice versa in selected in a range of from 1 milliseconds to 300 milliseconds. In the present embodiment, such duration of time is selected to be about 5 milliseconds.
The PCM audio data developed at the output side of the cross-fader circuit 4 is supplied to a recording-system signal processing circuit 7, in which it undergoes addition of error correction code, interleaving modulation and the like. The PCM audio data thus processed by the processing circuit 7 is further supplied to a recording head 8, thereby recorded on multi channels, for example 8 channels of the magnetic tape 1. The PCM audio data developed at the output side of the cross-fader circuit 4 is also supplied to a digital-to-analogue (D/A) converting circuit 9, in which it is converted to an analog signal. This analog signal therefrom is supplied to an external output terminal 10.
With the above-noted circuit arrangement, the signals of 8 channels are generally processed in a time-division manner so that other circuit arrangements than the analogue-to-digital converting circuit 6 and the digital-to-analogue converting circuit 9 are prepared, respectively.
When the editing is performed by the recording and reproducing apparatus for PCM audio data shown in FIG. 1, the external output terminal 10 is connected to the input side of an analogue mixer circuit 11 which forms an editing operating apparatus, while the output side of the analogue mixer 11 is connected to the external signal input terminal 5. Thus, a desired editing is performed by the operation of the analogue mixer 11.
When the editing is performed by using the analogue mixer 11, each of the digital-to-analogue converting circuit 9 and the analogue-to-digital converting circuit 6 has a delay time of, for example, 250 microseconds so that a channel (track) in which PCM audio data derived from the analogue mixer 11 is recorded causes a time delay as compared with other channel (track). This causes the tone quality to be changed. This defect will be explained more fully.
Let it be assumed that, of audio tracks of 8 channels, a vocal signal is recorded on 2 channels and musical performances by various musical instruments are recorded on remaining 6 channels. In this case, the analogue mixer 11 is arranged to receive an audio signal applied to its external input terminal 30, and signals of 8 channels reproduced from the magnetic tape 1 by the reproducing head 2 are mixed by the analogue mixer 11 and fed to a monitor terminal 31 as a monitor audio signal. If now it is determined by checking the audio signal from the monitor terminal 31 that some portion of the vocal signal is distorted and is out of tune, at least this portion of the vocal signal has to be re-recorded and then corrected.
In that event, a singer sings while listening to a reproduced vocal signal from the monitor terminal 31 so that the phase of a vocal signal now being inputted by the singer may coincide with that of the reproduced vocal signal. Then, the vocal signal is inputted through the external input terminal 30 to the analogue mixer 11. However, the reproduced vocal signal which the singer can listen to is processed by the digital-to-analogue converting circuit 9 so that it has a small delay time of, for example, about 250 microseconds from the real reproducing time. Consequently, the vocal signal inputted to the analogue mixer 11 through the external input terminal 30 by the singer is delayed in time from the reproduced vocal signal by about 250 microseconds. Further, this vocal signal, inputted by the singer, is supplied from the analogue mixer 11 to the analogue-to-digital converting circuit 6, in which it is converted to the digital audio signal. This digital audio signal is supplied through the cross-fader circuit 4 and the recording-system signal processing circuit 7 to the recording head 8, thereby recorded on the magnetic tape 1. In this case, this digital audio signal is further delayed by about 250 microseconds by the converting operation of the analogue-to-digital converting circuit 6. As a result, the vocal signal is re-recorded with a total delay time of about 500 microseconds. If the editing using the analogue mixer 11 is repeatedly performed, then the delay time is increased accordingly.